تجزيه و تحليل و تشخيص عيب ناهم محوري در موتورهاي القايي قفسه اي

چكيده انگليسي :

126 Analysis and Detection of Eccentricity in Squirrel Cage Induction Motors Hossein Hooshmandi Safa h hoshmandisafa@ec iut ac ir Date of Submission 2011 04 13 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Mohammad Ebrahimi mebrahim@cc iut ac irAbstractThree phase induction motors with a wide range of power ratings ranging from a fraction of a kW up to afew MW are the key elements in many industry applications They are widely used in differentcommercial equipments Today it is very important to detect the fault as soon as it occurs This is to avoidaccidental and unpredictable shutdown of equipments due to the expansion of faults this matter shows itsimportance particularly in heavy motors which will lead to financial losses that cannot be recuperated Inaddition repairing such heavy motors is time consuming and costs a lot Mechanical faults normally occurbecause of the damage applied to the mechanical components of the motor such as bearings and gear box The probability of these faults in electrical motors is more common at about 50 to 60 The mostimportant mechanical faults are bearing faults 40 50 and eccentricity 60 Eccentricity results innon uniform air gap between the stator and rotor Eccentricity can be of static type dynamic type or acombination of both which is called mixed eccentricity In static eccentricity the rotational axis of the rotorcoincides with the symmetrical axis but it displaces from the stator symmetrical axis In this case the airgap distribution is not uniform around the rotor but it is time invariant In dynamic eccentricity the statorsymmetrical axis coincides with the rotor rotational axis but the rotor symmetrical axis displaces Air gapdistribution in this case is non uniform around the rotor and also time variant The static and dynamiceccentricities tend to coexist and mixed eccentricity must be considered in reality In this case the center ofrotor the center of stator and the center of rotation are displaced with respect to each other There are several methods to detect this fault Among them is motor current signature analysis which due toIts noninvasive and easy implementation has a wide usage In this project the initial goal is currentspectrum analysis in eccentricity condition Therefore first some common eccentricity fault diagnosismethods are introduced Fault indication indexes characteristics and problems are presented and then themethods are evaluated then the modified winding function approach to calculate the inductances is used this theory proposes an improved analytical method to calculate the inductances in induction motors Alsomodeling of the induction motor in faulty condition including the rotor and stator voltage and mechanicalequations are developed Then rotor slot harmonics and other harmonics related to eccentricity will beanalyzed and the way these harmonics are generated in current spectrum is investigated Differenteccentricity cases in motor current spectrum will be analyzed afterwards Also the effect of motor pole pairsand rotor bars numbers in detecting different types of eccentricity is investigated and their relation to theappearances of certain harmonics caused by static and dynamic eccentricity in the motor current spectrum isfurther discussed for example in a motor with 44 rotor bars and 4 poles fault harmonics which are the onesaround the rotor slots harmonics won t appear in the motor current spectrum Therefore the fault cannotbe detected Finally it is shown that the static eccentricity can be detected by observing the harmonic entityaround the fundamental frequency of motor current spectrum in non inherent symmetric motor In this casedifference between electrical resistances of the rotor bars which is caused by the manufacturing process causes some harmonic components around the fundamental frequency which are not present in symmetricalstates of the motor These harmonic

هوشمندي صفا، حسين

تجزيه و تحليل و تشخيص عيب ناهم محوري در موتورهاي القايي قفسه اي

ناهم محوري بين روتور و استاتور , تحليل طيف جريان موتور